The isolation of individual colonies of micro-organisms (and in particular bacteria) is an important procedure in many microbiological laboratories. Traditionally, this isolation of bacteria has been performed manually by skilled laboratory technicians who first dispense a microbiological sample onto the surface of a solid growth culture medium, such as agar in a Petri dish (which will hereafter simply be referred to as a “medium” in an “agar plate” or simply in a “plate”), followed by the use of a hand-tool to spread the sample across the surface of the medium (called “streaking”).
The hand-tool typically includes a terminal loop to make multiple streaks of increasing dilution of the inoculum across the medium. The streaks of increasing dilution tend to provide, generally towards the tail of the streaks, a number of single cells that allow for the growth of isolated microbiological colonies after incubation. These isolated colonies may then be analysed for colony morphology, and may undergo staining and other procedures which are necessary for determining, for example, the genus, the species and the strain of the previously unidentified organism.
Such inoculation and streaking is highly repetitious and in many pathology diagnostic microbiology laboratories is usually conducted in very high volumes, such as in volumes as high as 1,000 to 15,000 plates per day. It is tedious and laborious work that therefore is prone to error and inaccuracies. It is quite obviously work that would lend itself to either partial or full automation.
The literature is replete with suggestions for how best to automate these laboratory functions, yet very few of these suggestions have ever actually found success in a commercial laboratory environment. It therefore appears that the successful enablement of suitable laboratory apparatus has to date, for most, proved elusive.
A sample of patent documents that, since the early 1970's, have suggested different apparatus for automating the inoculation and streaking of solid growth media are U.S. Pat. No. 3,778,351 (R. J. Rosov) titled “Automatic Bacterial Specimen Streaker”, U.S. Pat. No. 3,844,896 (A. N. Sharpe) titled “Apparatus for Performing Bacteriological Tests Automatically”, U.S. Pat. No. 3,850,754 (J. R. Wilkins et al) titled “Automatic Inoculation Device”, U.S. Pat. No. 3,935,075 (R. C. Perry et al) titled “Automatic Bacterial Specimen Streaker and Method for Using Same”, U.S. Pat. No. 4,144,135 (P. J. L. Sequeira) titled “Spreader Device and Method of Spreading Inoculant”, U.S. Pat. No. 4,287,301 (T. W. Astle) titled “Method and Apparatus for Streaking Agar”, and U.S. Pat. No. 4,613,573 (K. Shibayama et al) titled “Automatic Bacterial Colony Transfer Apparatus”. To the best of the applicant's knowledge, none of these suggestions have been successfully enabled, and thus suitable automation is still not available for such inoculating and streaking.
Three further, more recent, suggestions from the prior art require some discussion. They are the suggestions made by Vista Laboratories Ltd in U.S. Pat. No. 4,981,802 (C. Wylie et al) titled “Method and Apparatus for Streaking a Culture Medium”, the Canadian Space Agency in U.S. Pat. No. 6,617,146 (F. Naccarato et al) titled “Method and Apparatus for Automatically Inoculating Culture Media With Bacterial Specimens From Specimen Containers”, and Medvet Science Pty Ltd in international patent publication WO2005/071055 titled “Microbial Streaking Device” (licensed to the present applicant).
The Wylie patent describes an apparatus that only partially automates the inoculation and streaking process, in that it provides an apparatus for streaking a solid growth culture medium that has been manually inoculated by a laboratory technician, with the laboratory technician manually identifying upon the side of a plate the physical location of the inoculum (which identifying mark is later sensed by the streaking mechanism to determine where to commence streaking from). Furthermore, the streaking mechanism suggested for use by Wylie is a complex multiple head mechanism that relies on multiple passes across the medium by a single-point tool so as to provide a sinuous streaking path. The Wylie apparatus is thus reasonably slow and provides only a partial response to the automation challenge.
The Naccarato patent describes an automated process for single-point inoculation of a solid growth culture medium (at any location on the surface) from one of a possible variety of different forms of specimen container, followed by the subsequent use of a traditional, single-point streaking tool again following a convoluted path across the surface of the medium to thereby spread the inoculum. So that the streaking tool knows where the inoculum will be on the surface, the Naccarato apparatus describes the use of a reasonably complex device for recording the precise location of the inoculum, once the inoculum is placed on the surface, for use in subsequently guiding the streaking tool to that recorded location. These intermediate recordal and guiding steps, intermediate in the sense that they occur between inoculation and streaking, appear to introduce an undue risk of error and also unnecessary delays in the overall process.
The Medvet Science publication seeks to improve the automation process by the use of a new form of streaking tool, which tool includes a line of spaced apart contact surfaces (for contact with the surface of solid growth culture media), the contact surfaces being resiliently flexibly supported by a common support member. This streaking tool permits greater spread of a larger volume of the inoculum across the surface of the medium with a single streaking pass, as well as larger areas of more gradually increasing dilution of the sample. The inoculating and streaking apparatus described in the Medvet Science publication suggests the use of a pressure sensor to determine when the contact surfaces of the streaking tool have contacted the surface of the medium, without describing how the streaking tool knows the location of the inoculum on the surface (in terms of both two dimensional and three dimensional space).
It is an aim of the present invention to provide an automated apparatus for the inoculation and streaking of a microbiological sample on the surface of a solid growth culture medium, together with a method for the inoculation and streaking of a microbiological sample on the surface of a solid growth culture medium.
Before turning to a summary of the present invention, it must be appreciated that the above description of the prior art has been provided merely as background to explain the context of the invention. It is not to be taken as an admission that any of the material referred to was published or known, or was a part of the common general knowledge in Australia or elsewhere.
It is also useful to provide an explanation of some of the terms that will be used to define the spatial relationship of the apparatus and various parts thereof. In this respect, spatial references throughout this specification will generally be based upon a plate ultimately being inoculated and streaked in an upright orientation, with the surface of the medium in the plate being generally flat and horizontal. With this environment as the basis, the apparatus and some parts thereof may then be defined with reference to the “horizontal”, allowing further references to “upper” or “upwardly” and “lower” or “downwardly”, and also to the “vertical”. In this respect, the traditional geometric spatial reference to x,y and z dimensions, and then to the x direction (or axis), the y direction (or axis) and the z direction (or axis), will also be adopted, with the x and y directions lying generally horizontally and the z direction lying generally vertically.
Finally, some aspects of the present invention that may ultimately be claimed in isolation (and not in an in-use environment), may nonetheless be difficult to describe and understand in isolation. Thus, some of the following description does describe the invention and its embodiments in such an in-use environment (for example, with a plate carrying medium within the apparatus for the purposes of inoculation and streaking). Of course, it must be appreciated that the use of such description, and the use of the abovementioned spatial relationships, to define the present invention, is not to be seen as a limitation and certainly is not to be seen as a limitation only to the in-use environment, unless that is clearly stated to be the intention.